https://github.com/michaliskambi/x3d-tests/wiki/Incompatibility-in-how-relative-URLs-are-resolved%2C-when-used-together-with-EXTERNPROTO
https://github.com/michaliskambi/x3d-tests/tree/master/relative_urls_in_externproto/working_in_instantplayer_and_view3dscene